Richard Taylor, Extension Agronomist; rtaylor@udel.edu
Many equine and animal producers are running close to the edge this year with hay supplies since the frequent and heavy rainfall last summer either resulted in lower quality hay or prevented hay making completely. Grazers as well as hay producers should consider fertilization of their fields as soon this spring as soil conditions permit. The heavy rainfall last fall and over the winter months has leached nitrogen (N) and sulfur (S) from the upper rooting zone in pastures and hay fields.
Nitrogen application boosts the growth rate of the grass component in pastures and hay fields and with the very cold start to spring this year and the short hay supplies most producers will want to get their pastures and hay fields off to a rapid start. At least in the northern portion of Delaware, pastures and hay fields are just beginning to green up and start spring growth. With warmer temperatures and drier conditions expected until Tuesday of next week, now is the time to fertilize pasture and hay fields. Many producers will be using urea (46-0-0) as their primary N source but since S has leached out of the upper rooting zone in the soil, I suggest that producers consider applying at least a portion of the required N as ammonium sulfate. Application of both nutrients will ensure that the proper N to S ratio is available so that the sulfur containing amino acids are produced by the plant. Ammonium sulfate is the most acidifying of the N fertilizers but the proper N:S ratio is required by pasture plants.
If the pasture or hay field has a significant amount of legume (white, red, or alsike clover or alfalfa) present, you should limit the N rate to 20 to 30 lbs N/acre and in that case I would use 100 percent as ammonium sulfate. For pure grass hay fields or pastures with less than 25% legumes, apply about 50 lbs of N/acre per ton of expected yield. Apply about half of the N from ammonium sulfate but once the S application rate reaches about 40 lb S/acre change back to pure urea or other N source. You are unlikely to see a response past the 40 lb S/acre/year rate.